1. Field of the Invention
The present invention relates to a method for driving a plasma display panel (hereinafter designated xe2x80x9cPDPxe2x80x9d) which employs a matrix display scheme.
2. Description of Related Art
As a type of PDP employing such a matrix display scheme, known is an AC (alternating current discharge) type PDP.
The AC type PDP comprises a plurality of column electrodes (address electrodes) and a plurality of row electrodes, orthogonal to the column electrodes, and a pair of row electrodes forming a scan line. Each of these row and column electrodes is coated with a dielectric layer exposed to a discharge space, and an intersection of a row electrode and a column electrode define a discharge cell corresponding to one pixel.
With this construction, PDP operates by discharge phenomenon and thus the aforementioned discharge cell has only two states, that is, a xe2x80x9clight-emittingxe2x80x9d state and a xe2x80x9cnon-light-emittingxe2x80x9d state. Accordingly, in order to implement brightness display of halftone with such a PDP, a sub-field method is employed. According to the sub-field method, the period of one field is divided into N sub-fields and each of the sub-fields is assigned with a light emitting period (the number of light emissions) corresponding to the weight assigned to each bit digit of pixel data (N bits) for light-emission.
For example, as shown in FIG. 1, in the case where one field period is divided into 6 sub-fields, SF1 through SF6, light is emitted with the following ratio of light emission periods. That is,
SF1: 1
SF2: 2
SF3: 4
SF4: 8
SF5: 16
SF6: 32
For example, when the discharge cell is to emit light at brightness xe2x80x9c32xe2x80x9d, only SF6 of sub-fields SF1 through SF6 is allowed for emitting light. For light emission at brightness xe2x80x9c31xe2x80x9d, sub-fields SF1 through SF5, except for sub-field SF6, are caused to emit light. This enables brightness expression with 64 levels of halftone.
In cases where the discharge cells are caused to emit light at brightness xe2x80x9c32xe2x80x9d and at xe2x80x9c31xe2x80x9d, light emission drive patterns are inverse with each other in one field period. That is, within one field period, during the period when the discharge cells that are to emit light at brightness xe2x80x9c32xe2x80x9d are emitting light, the discharge cells that are to emit light at brightness xe2x80x9c31xe2x80x9d are in a xe2x80x9cnon-light-emittingxe2x80x9d state. On the other hand, during the period when the discharge cells that are to emit light at brightness xe2x80x9c31xe2x80x9d are emitting light, the discharge cells that are to emit light at brightness xe2x80x9c32xe2x80x9d are in a xe2x80x9cnon-light-emittingxe2x80x9d state.
Therefore, presence of a region where a cell that is to emit light at brightness xe2x80x9c32xe2x80x9d is adjacent to a cell that is to emit light at brightness xe2x80x9c31xe2x80x9d may cause a quasi-contour to be noticed in this region. That is, suppose that line of sight from the cell that is to emit light at brightness xe2x80x9c32xe2x80x9d, immediately before the cell changes from the non-light-emitting state to the light-emitting state, is moved to the cell that is to emit light at brightness xe2x80x9c31xe2x80x9d. In this case, only the non-light-emitting state of both cells is continuously viewed, thereby causing a dark line to be viewed on the boundary of both. Therefore, this dark line appears on the screen as a quasi-contour that has nothing to do with pixel data, thereby degrading the display quality.
Furthermore, as mentioned above, PDP employs discharge phenomenon and thus discharge (accompanying light emission) which has nothing to do with the contents of the display being be performed. This also presented a problem in that the contrast of picture images is degraded. Still furthermore, at present, there is a general theme of implementing low power consumption in manufacturing such PDP.
The present invention has been developed to solve the aforementioned problems. Its object is to provide a method for driving a plasma display panel that can provide improved contrast at low power consumption while preventing quasi contours, and improved display quality by stabilizing selection discharge.
The method for driving a plasma display panel, according to a first aspect of the present invention, is characterized in that the plasma display panel comprises pairs of row electrodes arrayed for each scan line and a plurality of column electrodes arrayed intersecting the respective row electrodes, wherein respective discharge cells are formed corresponding to respective pixels at respective intersections of pairs of the row electrodes for the respective scan lines and the plurality of column electrodes and wherein N sub-fields form a display period of one field, with M (2xe2x89xa6Mxe2x89xa6N) sub-fields occurring successively within the N sub-fields being taken as a sub-field group; executed are a reset process for generating discharge for initializing all the discharge cells into a light-emitting cell state only in the head sub-field in the sub-field group, a pixel data write process for applying pixel data pulses to the column electrodes for generating discharge to set the discharge cells to non-light-emitting cells in any one of the sub-fields within the one field and for applying scan pulses to one of the pair of row electrodes in synchronization with the pixel data pulses, and a light-emission sustain process for generating discharge for causing only the light-emitting cells to emit light only for a light-emission period corresponding to a weight of the sub-field in respective sub-fields within the sub-field groups; and sub-fields of a plurality of sub-groups classified according to waveforms of the scan pluses of respective sub-fields exist in said sub-field group and at least one of the pulse widths and pulse voltages of the scan pulses within sub-fields belonging to a first sub-group including at least a head sub-field of the sub-field group is set larger than respective values of the same of the scan pluses within a sub-field belonging to another sub-group.
The method for driving a plasma display panel, according to a second aspect of the present invention, is characterized in that the plasma display panel comprises pairs of row electrodes arrayed for each scan line and a plurality of column electrodes arrayed intersecting the respective row electrodes, wherein respective discharge cells are formed corresponding to respective pixels at respective intersections of pairs of the row electrodes for the respective scan lines and the plurality of column electrodes, and wherein N (N is an integer equal to 2 or more) sub-fields form a display period of one field; executed are a reset process for generating discharge for initializing all the discharge cells into a light-emitting cell state only in the head sub-field in the one field, a pixel data write process for applying pixel data pulses to the column electrodes for generating discharge to set the discharge cells to non-light-emitting cells in any one of the sub-fields within the one field and for applying scan pulses to one of the pair of row electrodes in synchronization with the pixel data pulses, and a light-emission sustain process for applying sustain pulses to the row electrodes alternately and sequentially in order to generate discharge for causing only the light-emitting cells to emit light only for a light-emission period corresponding to a weight of the sub-field in respective sub-fields within the one field; and at least one of the pulse widths and pulse voltages of the sustain pulse to be applied finally at the light-emission sustaining process is set larger than the pulse width and pulse voltage of the sustain pulse to be applied at some midpoint in the same light-emission sustaining process.
The method for driving a plasma display panel, according to a third aspect of the present invention, is characterized in that the plasma display panel comprises pairs of row electrodes arrayed for each scan line and a plurality of column electrodes arrayed intersecting the respective row electrodes, wherein respective discharge cells are formed corresponding to respective pixels at respective intersections of pairs of the row electrodes for the respective scan lines and the plurality of column electrodes, and wherein N (N is an integer equal to 2 or more) sub-fields form a display period of one field into, with M (2_ . . . M_ . . . N) sub- fields occurring successively within the N sub-fields being taken as a sub-field group; executed are a reset process for generating discharge for initializing all the discharge cells into a light-emitting cell state only in the head sub-field in the sub-field group, a pixel data write process for applying pixel data pulses to the column electrodes for generating discharge to set the discharge cells to non-light-emitting cells in any one of the sub-fields within the sub-field group and for applying scan pulses to one of the pair of row electrodes in synchronization with the pixel data pulses, and a light-emission sustain process for applying sustain pulses to the row electrodes alternately and sequentially in order to generate discharge for causing only the light-emitting cells to emit light only for a light-emission period corresponding to a weight of the sub-field in respective sub-fields within the sub-field group; and at least one of the pulse widths and pulse voltages of the sustain pulse to be applied finally at respective light-emission sustaining processes in the sub-field group is set larger than the pulse widths and pulse voltages of the sustain pulse to be applied at some midpoint in the same light-emission sustaining process.